A pair of descending neurons with dendrites in the optic lobes projecting directly to thoracic ganglia of dipterous insects

The lobula descending neuron (LDN) of dipterous insects is a unique nerve cell (one on each side of the brain) that projects directly from the lobula complex of the optic lobes to neuropil in thoracic ganglia. In the supraoesophageal ganglia the LDN has two prominent groups of branches of which at least one is dendritic in nature. Postsynaptic branches are distributed in the lobula and some branches, the synaptic relations of which are not yet known, extend to the lobula plate. A second group of branches is found among dendrites of the descending neurons proper, in the lateral midbrain. The arborizations of LDN in the lobula (and lobula plate) map onto a retinotopic neuropil region subserving a posterior strip of the visual field of the compound eye. The arborizations in the lobula complex are extremely variable in size. The numbers of dendritic spines they possess vary greatly between left and right optic lobes of one animal, and between individual animals.